The Paradox Echo
by owlwayssandforever
Summary: The Doctor and Clara land in a very strange land, unsure of how they arrived. A mysterious box appears in the middle of Gryffindor quidditch practice.


**House:** _Ravenclaw_ **| Year:** _1_ | **Category:** _Crossover_ **| Prompt:** _Doctor Who_ **| Word Count:** _1608  
_Hogwarts School Insane Prompt Challenge | House: Gryffindor | Prompt: 748 - Fandom - Doctor Who_  
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A high-pitched, pulsating whine whirred through the air, making everyone on the Quidditch pitch turn and look for the source of the noise. A tall blue box marked 'Police' had appeared under the far goalposts, much to everyone's confusion. The seven Gryffindors touched down on the ground, following their captain as they drew closer to the strange box. The door opened with a sudden _bang_, and a man with silver hair and angry eyebrows stumbled out.

"We're in Scotland, I'm sure of it!" he shouted back towards the box. "The air smells like Scotland, well, it smells _almost _like Scotland."

"So does that mean we're not in Scotland at all?" a young woman asked, poking her head out of the door.

"No, we're definitely in Scotland," the man said, his voice drifting off as he noticed the seven Gryffindors standing and staring at them. "But perhaps a different Scotland…"

"What do you mean?" the young woman pressed, skipping out of the box to stand next to him. "Is this like New New York? New New Scotland?"

"No, I think… Clara, I think we might have gone to a parallel universe…" He was looking at her from the corner of his eyes, his voice low, as though he thought that if he were completely still and quiet enough, the seven Gryffindors might not notice him.

"Doctor? What do you mean a _parallel universe_?" she hissed, placing her hands on her hips. She was tiny in stature, but her ferocity rivaled Ginny's. "We can get home, right?"

"Probably," the Doctor shrugged.

"Probably? We better be able to!" she threatened. "Danny's going to kill me."

"Oh, don't worry about PE," the Doctor dismissed, "maybe there's a better one on this Earth."

"He's a maths teacher!"

"Um, excuse me," Harry said, stepping forward at last. He'd had enough of their bickering and he wanted answers. "Who exactly are you? And how did you get here? You can't Apparate into school grounds…"

"I'm the Doctor," the man replied, turning his intense stare on Harry, "and this is—"

"Clara Oswald," the woman interjected, stepping forward and holding her hand out to shake.

"—my companion," the Doctor finished, and she shot him a look.

"We're travelers," Clara explained, "and we actually got here by accident. Would you mind telling us where we've ended up, and, er, when?"

"You're at Hogwarts," Harry said, suspicious of the new arrivals, "and it's 1996."

"What's Hogwarts?" the Doctor asked, looking at the scenery around him as if he were searching for clues to something.

"Hogwarts School of Witchcraft and Wizardry," Harry answered.

"I thought all wizards knew about Hogwarts, especially the Scottish ones," Ginny remarked snidely from his side.

"Ah, we're not wizards," Clara replied with a smile. "Well, I'm not. He might be, if you expand your definition of wizard a bit… Not your type of wizard though, in any rate."

Harry's fingers tightened around his wand reflexively.

"What do you mean he's not _my type _of wizard?"

"I just meant, well, he's got two hearts and can put a kid to bed in a jiffy, but there's no magic wand or pointy hat," Clara said.

"He's got two hearts?" Harry asked, incredulous. He thought he knew about all the humanoid beings, but he'd never heard of any with two hearts.

"Time Lord," the Doctor answered, sounding bored. He was looking at the broomsticks they all held in their hands with curiosity.

"Ginny, go talk to Professor McGonagall, please; everyone else, back to the common room, practice is over," Harry announced in his booming captain's voice.

Demelza and Dean flanked Ginny as they walked away, leading Peakes and Coote. Ron stayed by Harry's side for a moment longer, but after sharing a significant look, he departed in the direction of Hagrid's hut. Harry knew he was using one of the many owls that often lingered there to send a message to Hermione.

"What did you mean when you said this was a parallel universe?" Harry asked, eyeing the newcomers with suspicion.

"Surely you know the theory of the multiverse?" the Doctor answered with about the same amount of care and attention as if he were swatting aside a bothersome fly.

"The what?"

"My god, your universe is primitive," he huffed, clearly exasperated, and Harry felt his hackles rise a bit at the insult.

"Doctor!" Clara hissed, giving him a pointed look.

"According to the theory of the multiverse, which is factual and not really a theory at all," the Doctor explained, rolling his eyes slightly, "there exists infinite universes, all different from each other in small ways. For every decision that you make, there is a universe where you make a different one—these universes are considered to be parallel universes. They exist alongside each other, with no intersection, or path between them."

"Then how did you get here?" Harry asked.

"I have the TARDIS," the Doctor said, his answer clarifying absolutely nothing.

"It's basically a time machine," Clara explained. "It can move anywhere in time and space, and it's bigger on the inside."

"Oh now you've ruined it," the Doctor whined loudly, and Clara shot him a glance that did absolutely nothing to deter him. "I look forward to people saying that every time, and now you've gone and ruined the surprise for the pudding-brain."

"I wasn't aware we were taking him for a ride," she challenged.

"So, you're telling me there are different worlds for every different situation?" Harry asked, returning to the topic at hand to make sure he understood.

"Yes, yes, one where there's no magic, one where you wore a blue cape-thingy today instead of a red one, one where—"

"My parents are alive," Harry finished, and the Doctor immediately stopped talking.

"Yes," Clara breathed after a long moment of silence.

"You can't go there," the Doctor said firmly. "I can't take you there."

"Why not?"

"It's not… They're not…" He seemed to be lost in his mind, as if he were traveling backward through the years and remembering something long ago shoved into some dark corner.

"Doctor?" Clara prompted softly.

"That's how it started. A universe where Pete Tyler lived," the Doctor said, talking more to himself than anyone else. "And then the Cybermen came, and the Daleks."

"But you got rid of them," Clara reminded him, her hand resting on his arm.

"And it cost everything," he replied cryptically.

"What's a Dalek?"

Hermione had appeared behind Harry, with Ron by her side. Harry didn't know how much of the conversation they had heard, but he didn't really care too much. There was nothing about this that they couldn't know. And Hermione would be able to understand much more of this situation than he could.

"Trust me, you don't want to know," Clara intoned, shaking her head.

"What about in this universe?" Harry pressed. "Could you travel back in time in this universe?"

"I don't know," the Doctor said, angry eyebrows furrowing even closer together. "The rules are a bit trickier when you cross realms, I've never tried it before. I don't even know how or why we got here yet. And I'm not in a rush to leave until I find out."

"If I help you, will you take us?" Harry bargained. "Will you try?"

"Harry, I don't know if that's a good idea," Hermione interrupted. Her voice was thick with concern, and Harry knew that if he looked back he was going to see the expression she wore so often around him these days. It was a mix of pity and worry, and it made him sick to his stomach.

"I have a chance, Hermione, I'm not going to let it go," Harry snapped.

"If you prove to be useful, I'll try to take you," the Doctor agreed. He walked away, muttering to himself and leaving behind Clara, Harry, Ron and Hermione.

"What are you going to do, Harry?" Hermione asked. "Try to kill Voldemort back then? Save your parents?"

"Of course he is," Ron spoke at last, cutting of Harry as he whirled to face them. "Why shouldn't he?"

"Because, it could change everything!" she hissed. "If he kills Voldemort back then, it would change the course of history."

"But things would be better, Hermione," Harry insisted.

"You don't know that," Hermione said.

"How could it possibly be worse?" Harry argued, wanting to scream. "All those people who wouldn't die - you think that's worse?"

"You don't know what would happen, Harry," she said, shaking her head. "What if it creates a paradox - if you kill Voldemort back then and your parents live, you'd be a different person, and then who goes back in time to kill him? None of the events that cause you to go back happen, so why would you? It's an impossible loop, Harry, and I don't know what happens then... and neither do you."

"The universe explodes," Clara interrupted, stepping forward. "Well, implodes, I guess, or both, I don't really know. But it ceases to exist, rather violently. That's what happens if you create a paradox of that magnitude. I don't recommend it."

Harry, Ron, and Hermione blanched.

"Fine," Harry consented, nodding his head. "But at least let me go see them. They don't have to know who I am, but just some time…"

"Won't that be torture, mate?" Ron asked, blue eyes searching his best friend.

"Not more than sixteen years without ever knowing them," Harry answered.

Ron and Hermione both nodded, accepting his words, but Harry didn't miss the worried look exchanged between them. As long as they helped him, he didn't care. He needed to do this.


End file.
